[feat] FocusManager: wrap around horizontally (#6315)
[feat] FocusManager: wrap around horizontally (#6315)

There doesn't seem to be a reason not to, but it could be limited to `Device:hasFewKeys()` if desired.

Cf. <https://github.com/koreader/koreader/pull/6312#issuecomment-650207697>.
Frenzie/koreader,Markismus/koreader,poire-z/koreader,NiLuJe/koreader,koreader/koreader,pazos/koreader,Hzj-jie/koreader,NiLuJe/koreader,koreader/koreader,poire-z/koreader,Frenzie/koreader,mwoz123/koreader